Field of the Invention
The present invention relates to an imaging apparatus, a method of driving an imaging apparatus, and an apparatus using the imaging apparatus.
Description of the Related Art
Imaging apparatus, such as a CMOS image sensor, are required to improve the operation speed of reading a pixel signal by a read circuit. In the Japanese Patent Application Laid-Open No. 2010-28320, it is described that a bias current of a transistor configured to amplify the signal voltage of a pixel is increased for a given period, thereby being capable of reading the pixel signal at a higher speed. In the Japanese Patent Application Laid-Open No. 2006-186467, it is described that a read current source portion is configured to supply a normal reading current and also temporarily supply an additional reading current, thereby being capable of reducing a read-out time.
In the Japanese Patent Application Laid-Open No. 2010-28320, as a method of increasing the bias current, a switch (transistor) of a constant current circuit configured to supply the bias current to the amplifier transistor is operated to change the current. Such a current path involves a parasitic capacitance, and hence a charge current for charging the parasitic capacitance is necessary at the time of the switching. In other words, a part of the current increased by the switching is used as the charge current. Accordingly, it takes a longer time for an output voltage of the amplifier transistor to change, resulting in a longer settling time. Thus, there is a problem in that the pixel signal voltage is unstably read at a lower speed.
In the readout method disclosed in the Japanese Patent Application Laid-Open No. 2006-186467, a load control signal is controlled to increase an operating current for a given period of time. Switching noise is generated when the load control signal is switched, resulting in a longer settling time of an output signal voltage. Thus, there is a problem in that the pixel signal voltage is unstably read at a lower speed.